When it comes to who should feel in charge of their own money, Beyonce said it best: "All the single ladies, now put your hands up."

Nearly all single women — 97 percent — said it's important to be engaged in managing their finances, according to a new Fidelity Investments study, "Single Women & Money."

However, three things are holding them back, the report found: underestimating their know-how, neglecting to plan for the future and saving too heavily in cash.

"Women are gaining a ton of financial power, but, they are too often in the back seat," said Alexandra Taussig, a senior vice president of women investors at Fidelity. Just 25 percent consider themselves primary decision-makers when it comes to family finances, according to a separate study from Fidelity.

Single women were less likely to consider themselves knowledgeable than other demographic groups on topics such as investing, retirement saving and creating a financial plan, Fidelity found.

"We have this lack of confidence," Taussig said.

Overall, 1 in 3 single women said they are concerned about their finances, compared with 1 in 5 single men.

"Women are gaining a ton of financial power, but they are too often in the back seat."-Alexandra Taussig, Fidelity Investments

Only 28 percent said they had a comprehensive financial plan in place to set savings goals and navigate paying down debt.

Over a third — and more than twice that of their male counterparts — said they keep half or more of their savings in cash primarily because they don't know where to invest it.

While zero-risk cash investments are entirely appropriate for short-term needs, such as an emergency fund, savers will lose money in the long run by trailing the rate of inflation. Alternatively, Taussig recommends an investment like a target-date fund, which automatically rebalances as retirement ages are reached.

At some point, most women will find themselves on their own. Aside from those who never marry or divorce, the average age of widowhood is 59, according to the Census Bureau, with many women living another decade or more beyond a husband's death.

To prepare for financial independence, "know what you owe, know what you own and know what your goals are," Taussig said. Then take the steps to get there, she added, including contributing to a 401(k) plan, building an emergency fund and reaching out to get help.

"That will make you feel more confident and in control," Taussig said.